1. Field of the Invention
This invention relates to systems used to retard abrasion of concrete railroad tie rail seats and the resilient pads upon which they are seated.
2. Background Information
Railroads use concrete crossties and resilient pads upon which the rails are seated. There is a long-standing problem of abrasion of the resilient pads and the concrete tie rail seats that has perplexed experts in the railroad industry for years.
Analyses of this long-standing problem have revealed that resilient pads, typically composed of elastomeric material such as rubber, polyurethane, ethylvinylacetate or high density polyethylene, deflect vertically and horizontally in a cyclically fashion under the loads imposed by the wheels of passing trains. The cyclical loads imposed upon the pads create relatively short term vertical load pulses that cause the face of the pad to oscillate horizontally on the ties. The inevitable presence of sand particles and other contaminants creates an abrasive laden slurry when moisture is introduced to the interfaces of the pads and adjoining crossties. Consequently, the normally expected life span of 35 or more years for a concrete tie is often reduced by half or more. This slurry also contributes to premature failure of the resilient pads. This invention will reduce abrasion forces that were exerted from the concrete to the resilient pad.
A number of unsuccessful solutions to the problem of the abrasion or erosion of concrete tie rail seats and resilient pads have been proposed. One solution is proposed by John Buekett in U.S. Pat. No. 4,925,094. He proposes the use of stainless steel or other non-corrodible metal or plastic plates that are substantially the same width as the rail base used between each tie and the associated resilient pad. The plate is rectangular, for example, 3 mm thick, and cast into the top surface of the tie so that the top surface of the tie is flush with the surrounding surface of the tie. In order to cast the plates into the tie, they are located in the tie mold before filling it with concrete. Each plate has lugs projecting downwardly from its underside, which provides a mechanical connection with the concrete body of the tie. The plate is substantially the same width as the rail flange and extends substantially across the full width of the tie beneath the rail flange. Also, the plate has a stiffness less than that of the concrete tie and a smooth upper surface. The Buekett solution has not been accepted in the United States because of the additional expense of manufacture and because erosive wear can occur near the peripheral edges of the plate and the resilient pad.
Another proposed solution to combat the abrasive or erosive wear of concrete railroad ties is disclosed in U.S. Pat. No. 5,110,046 to Hartley F. Young. Young's proposed solution is the use of an abrasion resistant plate (that in actual delivered product is a spring steel plate) forming a slip plane to allow the resilient pad to slip in cyclical loading without wearing the surface of the concrete. There are two methods that Young discloses. One method is for previously worn concrete surfaces and one method for slightly worn and new surfaces. The thickness of the abrasion resistant plate is preferably 1 mm. Young states two forms of the adhering material are an adhesive such as an epoxy resin or an HDPE closed cell foam pad of 1.5 mm thickness of the same size and shape as the plate.
The worn concrete method involves using an epoxy to adhere the concrete and resilient steel pad and provides a smooth surface for the resilient pad to move back and forth on horizontally without wear to the concrete or resilient pad. This method also enables the restoration of the rail seat where the abrasive forces had forced the removal of the grout from the rail seat. Anytime there is a void under the steel plate there are forces placed on the plate which will eventually lead to fracturing of the plate.
The other suggested solution involves using a closed cell HDPE gasket 1.5 mm thick as "a layer of adhering material". The gasket does not adhere the abrasion resistant pad to the concrete. The light density HDPE gasket pushes into the concrete surface and provides a smoother surface to the concrete on which the steel plate rests. The abrasion resistant plate is very stiff and subject to cracking and therefore failure. When the plate fails, it also produces a sharp knife like edge under the rail that cuts and quickly destroys the resilient pad. While the steel plate appears to retard abrasive wear of a tie and pad, it moves against the clamp with the eventual formation of cracks in the resistant steel plate. This solution has not been accepted in the United States because the bond between the adhesive and the steel plate or the concrete fails and allows the abrasive slurry to penetrate voids between the pad and the concrete. Similarly, the closed cell foam material suffers from the same deficiency. The (spring steel) "abrasion resistant plate" is subject to cracking when any uneven material or surface is between the concrete and "abrasion resistant plate". Any point loading of a spring steel plate will cause eventual failure.
The solutions proposed above, as well as all other known solutions in the prior art, have not economically solved the long-standing problem of premature wear of concrete cross ties caused by abrasion, erosion or corrosion in the rail seats.